Abrasive material



Patented June 19, 1945 NITED STATE s PATENT OFFICE ABRASIVE M ATERIALHal Fruth, Chicago, Ill., assignor to Galvin Manufacturing Corporation,Chicago, Ill., a cor- I poration of Illinois N Drawing. ApplicationApril 26, 1943, Serial No. 484,617

The present invention relates to improved loose granular abrasivematerials ofthe character used in the finish grinding of hard surfaces,and to improved methods of making such materials. This application is acontinuation-in-part of my 00- pending application Serial- No. 479,928,filed March 20, 1943. I

Inthe finish grinding of certain articlesy such,

for example, as piezoelectric crystals, it is nec-' essary to produceground surfaces which are substantially free from scratches or othersurface irregularities and are ground with precision accuracy topredetermined dimensions. From the standpoint of the per unit cost ofeach such grinding operation, it is desirable to use a low cost grindingmaterial and to reduce the time of each grinding operation to a minimum.It has been discovered that by tumbling 0r agitating the articles to beground in the presence of loose granular abrasive material, fast,uniform and accurate grinding is obtained with practically no laborcost. In utilizing this grinding method,

however, the particular abrasive material used is of the utmostimportance. Thus, each granule of the abrasive material must have weightand be provided with surfaces having a large number of small evenlydistributed cutting points, ifv the grinding action is to proceeduniformly and at the proper speed. Abrasive crystals or granules of thecorrect size and weight necessary to obtain fast cutting are not onlyexpensive, but in addition have a relatively small number of largecutting edges, with the result thatthey tend to scratch and chip thearticles with which they are brought into engagement during a tumblingoperation. Fine grinding powders are also very expensive and, althoughcapable of grinding without scratching 0r chipping the articles withwhich they are brought into contact, perform the desired cutting veryslowly. Moreover, if a mixture of fine/and coarse abrasive materials isused, the efiect of the fine material is lost, in that although a smallamount of cutting or abrading is produced thereby, the predominantvgrinding action is produced by the larger abrasive granules,

4 Claims.- (Cl. 51-1645) It is a still further object of the inventionto provide an improved and. exceedingly simple method of making anabrasive material having improved grinding characteristics.

Generally considered, the present. improved abrasive Or grindingmaterial is made up of a mass of granules or pellets of compositestructure, each of which includes a core or-body of. cheap, easilyobtainable material and a coat or surface layer formed of very finegrinding particles, which coat embraces all surface portions of the coreand is formed by cementing the particles of grinding material to thesurface of the core,

More specifically, the body material may consist of relatively coarsegranules of rock like material, such, forexample, as garnet, crushedquartz, gravel, or aluminum oxide aggregate, either of the fused orunfused variety, having diametefs ranging from .100" to .250".. Theabrasive coating which is applied to each granule of the body materialconsists of an admixture of a suitable bonding material, or binder,such, for

- example, as a sodium silicate cement, and the agent.

such that the surfaces of the articles are.

scratched or chipped to an extent not compen sated for by the grindingaction of the fine abrasive material.

It is an object of the present invention, therefore, to provide animproved grinding or abrasive material which is fast cutting, uniformlyabrades the surfaces of articles agitated therewith, and does notproduce scratches or other surface irregularities in the articles.

fine particles of a hard grinding medium, such,

for example, as silicon carbide, boron carbide or diamond dust.

In the preparation of the abrasive material,

the available body material is first sieved through sieves of thepropermesh in order to obtain granules having diameters within the rangespecified above, after which the selected body material is coated with asodium silicate cement, lead borate, or other suitable hinder or bondingthen allowed partially to-dry, after which they are mixed with an excessof the available grinding" powder or' material and the mixture isagitated by tumbling the'same in a ball mill or the like. The finegrinding material preferably consists of to 240 screen mesh boroncarbide, silicon carbide or diamond dust. After the granules of bodymaterial have thus been coated with the grindingmaterial, they areseparated.

from each other and allowed to dry, the separation being required inorder to prevent the The adhesive coated body granules are coated bodygranules from adhering to each other. After the abrasive coated granulesof body material hav dried sufficiently, they are baked at. a.temperature of approximately 300 degrees Fahrenheit for an interval oftimeysuf flcient to set the. cement and thus rigidly bond the particlesof grinding material to the surfaces of the body pellets.

Grinding material produced in the manner explained above is relativelyvery inexpensive because of the very small quantities of fine grindingpowders which are required to produce the rather extensive grindingsurfaces which coat the body pellets. In this regard, it is noted thatduring the tumbling or pebble milling of the adhesively coated bodygranules with the grinding powder, the surfaces of the granules areuniformly coated with the grinding powder, so that an exceedingly largenumber of very fine cutting points are formed on each unit surface areaof each body granule. Accordingly, when the abrasive material is mixedwith a batch of articles the surfaces of which are to be ground, and themixture is tumbled or otherwise agitated, the grinding of the articlesurfaces proceeds at a rapid rate without the production of surfaceirregularities in the articles. The speed of grinding may be attributedto the weight afforded by the body of pellets. The absence of surfacescratching and chipping may be attributed to the fact that only the veryfine cutting points of the exposed grinding powder enter into thegrinding operation, and to the additional fact that very low contactpressures are produced between the cutting points of the abrasivegranules and the surfaces of the articles being ground. In addition tothe advantages just mentioned, it is pointed out further that abrasivematerial of the character described may be separated from the articlesbeing ground with great cleanliness, such that little additionalcleaning of the articles is required after they have been separated fromthe abrasive material.

As indicated above, the improved abrasive material herein disclosed isparticularly applicable for use in the grinding of piezoelectriccrystals to predetermined dimensions, such that they are uniformlycharacterized by a predetermined resonant frequency characteristic. Inperforming such a grinding operation abrasive material formed in themanner described above may be mixed with 180 screen mesh carborundum inthe ratio of four parts of abrasive material to one part carborundum.This mixture is then introduced into a tumbling or ball milling jaruntil the jar is approximately one-half full, after which the desiredquantity of rough ground piezoelec tric crystals are introduced into themixture. When the jar is rotated at a' speed of from 30 to 40revolutions per minute, the crystals are rapidly and uniformly groundwithout chipping the edges thereof, without producing scratches or otherirregularities in the surfaces thereof, and with the production of anappreciable amount of chamfering of the corners and edges of thecrystals.

As a modification of the above-described method of making the abrasivematerial, it is pointed out that the cementing of the abrasive powder tothe granules of body material may,

if desired, be performed by a simple air drying, heat treating, fusionor vitrification of a mixture of the adhesive material, the bodymaterial, and the fine abrasive material or powder. In the latter casethe abrasive powder should preferably be intermixed with the hinder orbonding material before the vitrifying operation is started. If, morespecifically, a glazing material is used as the bonding agent, thismaterial should be mixed in the proper relative proportions with theabrasive materiakand the mixtur then remixed with the body granules. Themixture may then be heated to a vitrifying temperature, agitated asrequired, and then allowed to cool in order to produce a bond betweenthe body granules and the particles of abrasive material.

Although the-invention has been described as being particularlyapplicable to the finish grinding of articles with precision accuracy,it is pointed out that itjmay be also utilized to produce a buffing orpolishing material. To this end, body material formed of small pelletsor particles of leather, wood or another soft substance may bemixed-with a suitable bufling substance, such, for example, as whiterouge, lime or powdered stone. This compound may be either cemented orotherwise adhesively applied to the surfaces of the pellets of soft bodymaterial, or a loose mixture of the body material and the buffingcompound may be used. In either case, the polishing or buiflng operationis carried out by tumbling or otherwise agitating the articles to bepolished in the presence of the bufiing material as formed in the mannerjust explained.

While different embodiments of the invention have been described, itwill be understood that various modifications may be made therein, whichare within the true spirit and scope of the invention.

I claim:

1. A preformed abrasive material comprising relatively large pieces ofbody material each provided with a substantially uninterrupted surfacecoating which includes a mixture of relatively fine abrasive powder anda set bonding agent rigidly securing the powder particles to thesurfaces of the pieces of body material.

2. A preformed abrasive material comprising relatively large pieces ofbody material each provided with a substantially uninterrupted surfacecoating which includes to 240 screen mesh boron carbide particles and aset bonding agent rigidly securing the boron carbide particles to thebody piece surfaces.

3. A preformed abrasive material comprising relatively large pieces of arock-like mineral material each provided with a substantiallyuninterrupted surface coating which includes a mixture of relativelyfine silicon carbide and a set bonding agent rigidly securing theparticles of silicon carbide to the mineral piece surfaces.

4. A preformed abrasive material comprising pieces of aluminum oxidehaving diameters ranging from .125 inch to .250 inch and having theirrespective surfaces substantially uniformly coated with a mixtureconsisting of 180 to 240 screen mesh boron carbide particles and a setsodium silicate cement rigidly bonding the boron carbide particles tothe surfaces of said pieces.

. HAL F. FRUTH.

